Uncoated razor blades, despite their sharpness, cannot be employed for shaving a dry beard without excessive discomfort and pain, and it is as a practical matter necessary to employ with them a beard-softening agent such as water and/or a shaving cream or soap. The pain and irritation produced by shaving with uncoated blades are due to the excessive force required to draw the cutting edge of the blade through the unsoftened beard hairs, which force is transmitted to the nerves in the skin adjacent the hair follicles from which the beard hairs extend, and, as is well known, the irritation produced by excessive pulling of these hairs may continue for a considerable period of time after the pulling has ceased. Blade coatings were developed to solve these shortcomings.
Granahan et al., U.S. Pat. No. 2,937,976, issued May 24, 1960, describes a "coated" blade which provides a reduction in the force required to cut beard hair. The coating material consists of an organosilicon-containing polymer which is partially cured to a gel which remains adherent to the blade. Although these coated blades met with considerable commercial success, the coatings were not permanent and would wear off relatively quickly.
Fischbein, U.S. Pat. No. 3,071,856, issued Jan. 8, 1963, describes fluorocarbon-coated blades, particularly polytetrafluoroethylene-coated blades. The blades may be coated by (1) placing the blade edge in close proximity to a supply of the fluorocarbon and subsequently heating the blade, (2) spraying blade with a fluorocarbon dispersion, (3) dipping the blade into a fluorocarbon dispersion or (4) by use of electrophoresis. Example 2 shows a blade which is dip-coated with an aqueous colloidal dispersion containing 25% (wt) finely divided solid tetrafluoroethylene polymer (DuPont's Teflon Clear Finish). The resulting blade was later sintered.
Fischbein, U.S. Pat. No. 3,518,110, issued Jun. 30, 1970, discloses an improved solid fluorocarbon telomer for use in coating safety razor blades. The solid fluorocarbon polymer has a melting point between 310.degree. C. and 332.degree. C. and has a melt flow rate of from 0.005 to 600 grams per ten minutes at 350.degree. C. The molecular weight is estimated to be between 25,000 and 500,000. For best results, the solid fluorocarbon polymer is broken down to 0.1 to 1 micron particles. Example 2 discloses an aqueous dispersion of 0.5% polytetrafluoroethylene, PTFE, (Impurities: 0.44% Chlorine and 0.06% Hydrogen), and 0.5% Triton X-100 wetting agent. The dispersion is electrostatically sprayed onto stainless steel blades. Example 8 states that the polymerization of tetrafluoroethylene is achieved in an aqueous dispersion with methyl alcohol as the telogen and ammonium persulfate as the catalyst.
Fish et al, U.S. Pat. No. 3,658,742, issued Apr. 25, 1972, discloses an aqueous polytetrafluoroethylene (PTFE) dispersion containing Triton X-100 wetting agent which is electrostatically sprayed on blade edges. The aqueous dispersion is prepared by exchanging the Freon solvent in Vydax brand PTFE dispersion (PTFE+Freon solvent), distributed by E. I. DuPont, Wilmington, Del., with isopropyl alcohol and then exchanging the isopropyl alcohol with water. Example 1 discloses an aqueous PTFE dispersion containing 0.4% PTFE and 0.1% Triton X-100 wetting agent.
Dillon, U.S. Pat. No. 3,766,031, issued Oct. 16, 1973, incorporated herein by reference, indicates that the application of a critical dose of ionizing radiation to sintered or unsintered polytetrafluoroethylene renders such material capable of being comminuted to microfineness with no adverse heat side effects, and the resulting particles are readily dispersible in diverse media. Such particles possess the extremely low coefficient of friction associated with polytetrafluoroethylene resin. The dosage level of ionizing radiation in accordance with the process of this invention lies within the range of from about 5 megarads to about 25 megarads, and is preferably maintained between about 10 megarads and 25 megarads.
European Application No. 0 017 349, filed Mar. 6, 1980, discloses that sintered polytetrafluoroethylene can be nondestructively degraded so as to be grindable to a powder of an average size of less than 10 microns by a combination of irradiation by electrons or other subatomic particles in the presence of oxygen or air and concurrent or subsequent heating at temperatures below the melting point of the material. The preferred effective and economic range of irradiation, heat and time at temperature is approximately 50-150 Mrads, 150.degree. F. to 600.degree. F. for at least about one-half hour depending upon desired average particle size and melt flow characteristics and acceptable yields of the powders.
Previous attempts to employ aqueous polyfluorocarbon dispersions in blade coating processes have produced unacceptable adhesion or required unacceptably high force to cut hair. Furthermore, the polyfluorocarbon coating would wear off too rapidly as evidenced by a significant increase in the force required to cut or sever beard hair upon subsequent shavings.
An object of the present invention is to provide an environmentally-friendly method of coating razor blade edges with polyfluorocarbons, particularly polytetrafluoroethylene. Specifically, it is an object of the present invention to eliminate chlorofluorocarbon solvents and volatile organic solvents from the blade coating process.
It is also an object of the present invention to provide a razor blade cutting edge which produces substantially equal cutting and wear characteristics as chlorofluorocarbon dispersion-coated blades.
These and other objects will be apparent to one skilled in the art from the following: